Web Management User Guide
3
1 Introduction
Power-over-Ethernet (PoE) eliminates the need to run DC power to other devices on a wired LAN.
Using a Power-over-Ethernet system, installers only need to run a single Category-5 Ethernet
cable that carries both power and data to each device. This allows greater flexibility in the locating
of network devices and, in many cases, significantly decreases installation costs.
There are two system components in PoE - the PSE (Power Sourcing Equipment) and the PD
(Powered Device). The IEEE 802.3af/at specification defines PSE as a device that inserts power
onto an Ethernet cable. The PSE may be located at the switch (End-span configuration), or it may
be a separate device located between the switch and the PD (Mid-span configuration). The PD is
the natural termination of this link, receiving the power, and could be an IP phone, a WLAN
access point, or any other IP device that requires power. The current is transmitted over two of the
four twisted pairs of wires in a Category-5 cable.
Power-over-Ethernet follows the IEEE 802.3af/at specification and is completely compatible with
existing Ethernet switches and networked devices. Because the Power Sourcing Equipment (PSE)
tests whether a networked device is PoE-capable, power is never transmitted unless a Powered
Device is at the other end of the cable. It also continues to monitor the channel. If the Powered
Device does not draw a minimum current, either because it has been unplugged or physically
turned off, the PSE will shut down the power to that port. Optionally, the standard permits
Powered Devices to signal t0 the PSEs exactly how much power they need.
The PoE switch is a multi-port fast Ethernet switch that can be used to build high-performance
switched workgroup networks. This switch is a store-and-forward device that offers low latency
for high-speed networking. It also features a ‘store-and-forward switching’ scheme that allows the
switch to auto-learn and store source addresses in a 8K-entry MAC address table. The switch is
targeted at workgroup, department or backbone computing environments.
